To improve driving comfort, electromechanical steering systems of motor vehicles have power steering systems which introduce the assistance force generated by an electric motor into the steering column or the steering pinion and thus boost the force imparted by the driver when steering. In this case, the assistance force of the electric motor is transmitted to the steering pinion by means of a reduction gear mechanism, which may be in the form of a helical gear mechanism, worm gear mechanism or globoid gear mechanism.
The steering system-specific requirements demand that the reduction gear mechanism operates quietly without rattling and knocking and, in combination therewith, exhibits low friction. For this purpose, the tooth flank clearance of the reduction gear mechanism is minimized or eliminated.
A multiplicity of methods for minimizing the tooth flank clearance is known from the prior art.
To eliminate the clearance of the toothing engagement and at the same time permit a radial movement of the pinion, it is possible for the clearance to be set or readjusted for example by displacement of the pinion radially with respect to the gearwheel by means of one or more eccentrics. Furthermore, methods exist in which the pinion and the gearwheel are preloaded elastically against one another by way of suitable elastic elements. These methods permit compensation of concentricity tolerances of pinion and gearwheel, thermal expansion and wear.
In this case, the pinion axis is pivoted out of its central position, wherein the rear bearing arrangement itself, facing toward the motor, tilts. If the tilting of the bearing exceeds a threshold which is dependent on the bearing type and the bearing clearance, this leads to increased friction, severe fluctuations in friction, noises and a reduced service life of the bearing arrangement.
If it is assumed that the axial clearance of the bearings must be minimized in order to reduce steering knocking and rattling noises, the bearing types necessitated by this, such as for example four-point bearings, are even more sensitive to tilting.
It is therefore desirable, in particular also in the case of reduced axial clearance of the bearing, to permit tilting of the bearing without the abovementioned disadvantages.
Arrangements are known from the prior art for this purpose, which arrangements will be described below.
EP 2450262 A1 has disclosed a solution for the preloading of a worm gear mechanism, in which the bearing shells of the rolling bearing are designed such that the rolling bodies in the bearing shells permit an angular movement.
In the laid-open specification DE 10201002285 A1, the mounting of a helical pinion at a fixed bearing side is realized by way of a rolling bearing which permits a small pivot angle. Said pivoting is made possible by virtue of the outer bearing shell being received in a spherical cap-shaped bearing receptacle.
Furthermore, in DE 102008054441 A1, a solution is disclosed in which a convex outer bearing ring interacts with a resilient ring which permits elastic pivoting of the outer bearing ring. The bearing receptacle is in this case partially of concave form.
The patent application DE 102012005931, which does not constitute a previously published document, relates to a bearing which is damped in an axial direction. The bearing is received in a housing which has a projection of crowned form, whereby the bearing can perform a pendular movement.
It is an object of the present invention to provide a helical gear mechanism which has a bearing arrangement with improved characteristics.